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Enol
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Enol
In organic chemistry, enols are a type of functional group or intermediate in organic chemistry containing a group with the formula C=C(OH) (R = many substituents). The term enol is an abbreviation of alkenol, a portmanteau deriving from "-ene"/"alkene" and the "-ol". Many kinds of enols are known.
Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding electrons. The keto and enol forms are tautomers of each other.
Organic esters, ketones, and aldehydes with an α-hydrogen (C−H bond adjacent to the carbonyl group) often form enols. The reaction involves migration of a proton (H) from carbon to oxygen:
In the case of ketones, the conversion is called a keto-enol tautomerism, although this name is often more generally applied to all such tautomerizations. Usually the equilibrium constant is so small that the enol is undetectable spectroscopically.
In some compounds with two (or more) carbonyls, the enol form becomes dominant. The behavior of 2,4-pentanedione illustrates this effect:
Enols are derivatives of vinyl alcohol, with a C=C−OH connectivity. Deprotonation of organic carbonyls gives the enolate anion, which are a strong nucleophile. A classic example for favoring the keto form can be seen in the equilibrium between vinyl alcohol and acetaldehyde (K = [enol]/[keto] ≈ 3×10−7). In 1,3-diketones, such as acetylacetone (2,4-pentanedione), the enol form is more favored.
The acid-catalyzed conversion of an enol to the keto form proceeds by proton transfer from O to carbon. The process does not occur intramolecularly, but requires participation of solvent or other mediators.
If R1 and R2 (note equation at top of page) are different substituents, there is a new stereocenter formed at the alpha position when an enol converts to its keto form. Depending on the nature of the three R groups, the resulting products in this situation would be diastereomers or enantiomers.[citation needed]
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Enol
In organic chemistry, enols are a type of functional group or intermediate in organic chemistry containing a group with the formula C=C(OH) (R = many substituents). The term enol is an abbreviation of alkenol, a portmanteau deriving from "-ene"/"alkene" and the "-ol". Many kinds of enols are known.
Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding electrons. The keto and enol forms are tautomers of each other.
Organic esters, ketones, and aldehydes with an α-hydrogen (C−H bond adjacent to the carbonyl group) often form enols. The reaction involves migration of a proton (H) from carbon to oxygen:
In the case of ketones, the conversion is called a keto-enol tautomerism, although this name is often more generally applied to all such tautomerizations. Usually the equilibrium constant is so small that the enol is undetectable spectroscopically.
In some compounds with two (or more) carbonyls, the enol form becomes dominant. The behavior of 2,4-pentanedione illustrates this effect:
Enols are derivatives of vinyl alcohol, with a C=C−OH connectivity. Deprotonation of organic carbonyls gives the enolate anion, which are a strong nucleophile. A classic example for favoring the keto form can be seen in the equilibrium between vinyl alcohol and acetaldehyde (K = [enol]/[keto] ≈ 3×10−7). In 1,3-diketones, such as acetylacetone (2,4-pentanedione), the enol form is more favored.
The acid-catalyzed conversion of an enol to the keto form proceeds by proton transfer from O to carbon. The process does not occur intramolecularly, but requires participation of solvent or other mediators.
If R1 and R2 (note equation at top of page) are different substituents, there is a new stereocenter formed at the alpha position when an enol converts to its keto form. Depending on the nature of the three R groups, the resulting products in this situation would be diastereomers or enantiomers.[citation needed]
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